The study covered almost 4 million acres of irrigated agriculture and there are 1 million dairy cows within the study boundaries. Researchers claim 420,000 tons of nitrogen is applied annually, according to its models. Half of that is N applied to cropland, with only about 40 percent of the applied N harvested, suggesting that more than half the N applied is leached into the groundwater, a figure farmer’s find difficult to accept.

(For more, see: Fertilizer industry working to reduce groundwater pollution)

“With UN-32 at $442 per ton, I don’t think farmers are going to waste a lot of N,” said Kern County, Calif., pest control adviser Vern Crawford.

Tulare County, Calif., dairyman Tom Barcellos, a panelist at the workshop, also challenged the study’s tenor that farmers use more nitrogen than the crop needs by saying, “we have never made so much money that we can waste by putting on more than we need.”

Tulare County Board of Supervisors Chairman Allen Ishida urged caution in reacting to this study, calling for more scientific research to determine the exact source and age of the nitrogen in the groundwater.

Groundwater can be aged and some of the nitrate-tainted water could be 300 years old, contaminated by nitrates from foothill sediments washed into the groundwater basin by rainfall.

The model used to determine the source of nitrates seemed to be old and researchers acknowledged that they could not quantify the impact on such things as drip irrigation, conservation tillage and the fact that there is simply less water applied to crops today due to reduced surface water supplies. It is common knowledge that 100 percent of the processing tomatoes produced in the valley are grown with drip irrigation; 30 percent of the cotton is drip irrigated and virtually every new orchard or vineyard planted within the past 20 years is irrigated with low water volume micro-irrigation.

Barcellos said he is being forced to dig deeper wells due to the lack of surface water deliveries brought on by passage of laws giving farmers water for environmental uses. And, the deeper he goes, the higher the nitrate levels, suggesting that older farming practices are responsible for nitrate leaching, not today’s ag technology. This would imply over-regulating farmers now would do little to solve the age-old problem.

Ishida is a third-generation citrus farmer from the Lindsay-Strathmore area in Tulare County, the focal point of the study. He pointed out citrus growers no longer flood irrigate and therefore reduce leaching. They use micro-irrigation like drip and sprinklers to apply less water. “We (farmers) are already addressing the issue,” he said.

The researchers acknowledged advancement in farming, but did not seem to include them in outlining 50 management practices they claim could reduce nitrate use by 60 percent to 80 percent.